Cable stranding is a process in which individual wires are combined, typically in a helical arrangement, to produce a finished cable. The resulting stranded cable provides greater flexibility than is available from a solid rod of equivalent cross sectional area. The stranded arrangement is also beneficial because the stranded cable maintains its overall round cross-sectional shape when the cable is subject to bending in handling, installation and use. Such stranded cables are used in a variety of applications such as hoist cables, aircraft cables, undersea marine cables and tethers, and electrical power transmission cables.
Stranded electrical power transmission cables are typically produced from ductile metals such as steel, aluminum, or copper. In some cases, such as bare overhead electrical power transmission cables, a stranded wire core is surrounded by a stranded wire conductor layer. The stranded wire core could comprise ductile metal wires made from a first material such as steel, for example, and the outer power conducting layer could comprise ductile metal wires made from another material such as aluminum, for example. In some cases, the stranded wire core may be a pre-stranded cable used as an input material to the manufacture of a larger diameter electrical power transmission cable. Stranded electrical power transmission cables generally may comprise as few as seven individual wires to more common constructions containing 50 or more wires.
During the cable stranding process, ductile metal wires are subjected to stresses beyond the yield stress of the metal material but below the ultimate or failure stress. This stress acts to plastically deform the metal wire as it is helically wound about the relatively small radius of the preceding wire layer or core wire. There have been recently introduced useful cables made using composite wires made from materials that cannot readily be plastically deformed to a new shape, and which may be brittle.
One example of such composite wire cables is provided by a metal matrix composite wire cable containing fiber-reinforced metal matrix composite wires. Such metal matrix composite wires are attractive due to their improved mechanical properties relative to ductile metal wires, but which are primarily elastic in their stress strain response. Some polymer composite wire cables containing fiber-reinforced polymer matrix composite wires are also known in the art, for example, the fiber-reinforced polymer matrix composite wires disclosed in U.S. Pat. Nos. 4,961,990; 5,126,167; 7,060,326; 7,093,416; 7,179,522; 7,438,971; 7,683,262; and PCT International Pub. No. WO 97/00976.